Aluminum alloy



Patented May 23, 1933 UNITED STATES PATENT err-E FRED KELLER AND CHARLES'M. CRAIGHEAD, OF NEW KEN'SINGTON, PENNSYLVANIA,

ASSIGNORS TO ALUMINUM COMPANY OF AMERICA, OF PITTSBURGH, PENNSYL- VANIA, A CORPORATION OF PENNSYLVANIA ALUMINUM ALLOY v No Drawing.

This invention relates to aluminum base alloys which are possessed of high tensile properties, excellent resistance to corrosion, and the further property of retaining a sub- 5 stantial part of their original surface appearance after continued exposure to the atmosphere. There are uses of aluminum base uisites. Exemplaryof such uses are window frames. Such frames are often built up from extruded or rolled aluminum base alloy shapes. Since the distinctive color of aluminum lends itself readily to modern design, aluminum base alloys which will retain their natural color and appearance under constant exposure to ordinary or industrial atmospheres are in great demand.

29 The alloys must also, if adaptable to such uses, be of high strength and must likewise be resistant to corrosion in the sense that upon long exposure the tensile properties of the alloys do not materially depreciate.

The known high strength aluminum base alloys have, more or less, fulfilled the abovenoted requirements, but there has been .a need for an alloy whichwould combine, to a larger extent, hi h strength, corrosion- 30 resistance and a sta le surface appearance.

It is the general object of this invention to provide alloys of this nature.

Among the high strength aluminum base alloys which are best adapted to the uses and purposes above mentioned are the alloys described in the United States Patent No. 1,472,739 to Robert S. Archer and Zay Jeffries. The alloys described in this patent are characterized by the simultaneous presence therein of magnesium and silicon and primarily derive their good tensile properties from the action "and effect of these alloying elements under the influence of heattreatment and artificial aging. When magnesium and silicon are together present in alloys where high strength, good corrosion-resist. 10 ance and good appearance are primary req- Application filed September 21, 1932. Serial No, 634,152.

aluminum, they form a complex which is usually recognized as the intermetallic compound, Mg Si. The compound is to a certain extent soluble in the aluminum. When aluminum containingthis compound is thermally treated at temperatures above about 500 Centigrade but below the temperature at which incipient fusion takes place in the alloy, a portion of the Mg Si forms a solid solution with the aluminum, increasing the rosion-resistance and stable surface appearance is desired, thebest combination of these properties can be obtained when neicentigrade, the

ther an excess of magnesium nor an excess of silicon is present in the alloy, but that the magnesium and silicon .should'be present in such amounts as will combine sub- -stantially completely to form the intermetallic compound Mg si. Furthermore, as we have discovered, the alloy should contain 0.1 to 1.0 per vcent'by weight of chromium and should be compounded from alu- -minum which contains not more than 0.3

per cent by weight of impurities, said amount of impurities, of course, being exclusive of magnesium silicon or chromium.

The alloys contemplated by our invention are those which contain about 0.5 to 3.0 per cent by weight of Mg Si (or magnesium and silicon in amountand ratio to form such amounts of Mg S i), which contain no substantial excess of magnesium or silicon over the amounts necessary to form Mg Si and which contain 0.1 to 1.0 per cent by weight of chromium, the balance of the alloy being aluminum containing not more than 0.3 per cent by weight of impurities exclusive, of course, of silicon, magnesium and chromium. Alloys of this composition have tensile properties sufficiently high to meet many en gineering specifications. They have, more over, an excellent corrosion-resistance and stability of surface appearance. In this combination of properties they excel other high strength aluminum base alloys known and, in addition to these properties, alloys of this composition are readily worked into usual and even intricate forms and shapes.

The alloys above described may be heattreated and aged and otherwise thermally treated according to the methods known to the art and may by means of the known methods of working be fabricated into many shapes. The alloys may likewise be cast'according to usual foundry'practices.

Of the alloys which are the subject of this invention certain are preferred, especially as material from -which to form window frames and like articles. These are the alloys of higher strength which still retain excellent workability. These alloys contain about 1.5 to-2.0 per cent by weight of Mg si, 'f'about 0.1 to 0.5 per cent of chromium, 0.25

percent of'chromium being preferred, and the-balance being aluminum containing not more than about 0.3 per cent by weight of impurities exclusive of magnesium, silicon and chromium. These alloys have, in extruded form and .after heat-treatment at about 515 centigrade followed by cooling and artificial aging at about 160 centigrade for about 18 hours, an average tensile strength vof 35,000 to 39,000 pounds per square inch, an average yield strength of 30,000 to 34,000 pounds per square inch, and

an elongation of about 14 to 17 per cent in 2 inches.

It is a further beneficial property of the novelalloys herein described that they are, under the commercial methods of working and heat-treatment, singularly free from the 3. An alloy containing about 1.5 to 2.0 per cent by weight of the intermetallic compound Mg Si and about 0.25 per cent by weight of chromium, the balance being aluminum which does not contain more than 0.3 per cent by weight of impurity exclusive of magnesium, silicon and chromium.

In testimony whereof we hereto aflix our signatures.

FRED KELLER. CHARLES M. CRAIGHEAD.

phenomena of grain growth or large or uneven sized grains-and that, partly because of this .fact, they present in the worked condition a surface which is even and smooth.

We claim as our invention: a 1. An alloy containing about 0.5 to 3.0

aluminum which does not contain more than 0.3 per cent by weight of impurities exclusive of magnesium, silicon and chromium.

2. An alloy containing about 1.5 to 2.0

per cent by weight of the intern'ietallic comj ound Mg Si and about 0.1 to .-0.5 per cent y weight of chromium, the lial'an'ce being aluminum which does not contain more than 0.3 per cent by weight of impur ty excluslve of magnesium, siliconan'd chromium. 

